A conventional fire-blocking door lock structure as shown in FIG. 1 shows that a fire-blocking door lock 1 can be unlatched when a person presses a push handle 10a mounted on a frame member 10 that is horizontally mounted on the center of the fire-blocking door 2. When the push handle 10a is pressed down, a latch body 11 is withdrawn into the inside of a casing 3, unlatching the fire-blocking door lock 1.
To make the structure of the fire-blocking door lock 1 more understandable, the fire-blocking door lock 1 is rotated by 90 degrees such that the back faces downward as shown in FIG. 2. The frame member 10 comprises the push handle 10a mounted thereon for allowing the user to press it by hand and the casing 3 including the latch body 11 inside, which couples with one side of the frame member 10. The push handle 10a is mounted on two fixed supports 13 on the rear inside the frame member 10. Two slots 13 are respectively located on both side walls of each fixed support 13 for a sliding shaft 13b to be positioned in-between and further fixed on the side walls of the push handle 10a by a pin 13c on each end. Moreover, a spiral spring 13d is secured on the front rear of the fixed support 13 by a set pin 13e. Under normal conditions, the spiral spring 13d has one end abutting on the backside of the sliding shaft 13b applying an upward pressure thereon. When the push plate 10a is pressed down by hand, the sliding shaft 13b is forced to move inwards along the slots 13a, receiving the push handle 10a inside the frame member 10.
Referring to a dotted-line circle in FIG. 3, an actuating piece 13 mounted inside the casing 3 towards the front end of the frame member 10, has a driving portion 12a extended on one end and a passive portion 12b oppositely extended on the other end. The driving portion 12a has one end abutting on the inner part of the push handle 10a; whereas the passive portion 12b is in contact with a recess portion 11a inside the latch body 11 mounted in the casing 3. Hence, when the push handle 10a is pressed down, the driving portion 12a of the actuating piece 12 is forced to move downwards, thereby leveraging and impelling the passive portion 12b thereof on the other side to travel upwards. As the passive portion 12b moves, the end thereof abuts against the recess portion 11a of the latch body 11 causing the latch body 11 to turn in a counterclockwise direction; the latch body 11, as a result, is withdrawn into the inside of the casing 3 enabling the fire-blocking door lock 1 to be unlatched.
According to FIGS. 2 and 3, the inner structure of the casing 3 of the fire-blocking door lock 1 comprises a latching member 15 including both the previously mentioned latch body 11 and a safety latching member 14 mounted thereon, and a plate member 16 at the bottom of the latching member 15 to be mounted thereon. A pin 17 is utilized to pivotally couple the safety latching member 14 and the latch body 11 together on the top of the latching member 15, thereby enabling both the safety latching member 14 and the latch body 11 to pivot inside the latching member 15 round pin 17. The structure further enables spiral springs 18 and 19, respectively, to be pivoted at both sides of the latch body 11 by the pin 17.
Moreover, the spiral spring 18 has one end elastically pressed against the top of the latching member 15, and the other end elastically pressed against one end of the safety latching member 14. This allows the safety latching member 14 to protrude outside the latching member 15 when no external force is applied to the push handle 10a. The spiral spring 19 has one end pressing against the top of the latching member 15, and the other end thereof pressing against the inside of the recess portion 11a of the latch body 11. This also allows the latch body 11 to protrude outside the latching member 15 when no external force is applied to the push handle 10a. 
The safety latching member 14 of the fire-blocking door lock 1 further comprises a boss 14a on the side of the latch body 11. The boss 14a is abutted on an extended tongue-like piece 12c on the front of the passive portion 12b of the actuating piece 12, and a pin 20 is utilized to allow the actuating piece 12 to pivot on the latching member 15. Moreover, the fire-blocking door lock has a spiral spring 22 secured by a pin 21, which presses against the top of the actuating piece 12. This allows the actuating piece 12 to be positioned in a downward direction while no external force is being applied. In addition, the tongue-like piece 12c of the passive portion 12b and the boss 14a of the safety latching member 14 are pressed against each other. When the fire-blocking door is latched, the safety latching member 14 is pressed toward the doorframe and retracted to the inside of the latching member 15, thereby moving towards the inner latching member 15. Therefore, the boss 14a of the safety latching member 14 is disengaged from the position in contact with the tongue-like piece 12c on the front of the passive portion 12b. Consequently, the actuating piece 12 is forced downwards under elastic pressure by the spiral spring 22 so that the front end of the passive portion 12b of the actuating piece 12 is appropriately abutted against the inside of a stop portion 11b of the latch body 11. As a result, the latch body 11 can not be moved backwards and retracted into the latching member 15 due to the obstruction of the stop portion 11b. Therefore, the fire-blocking door 2 can be securely latched when the fire-blocking door lock 1 is under a normal lockup condition.
However, after being used over a long period of time, the structure of the fire-blocking door lock 1 result in a problem wherein a gap is formed between the door and doorframe when the door is latched; consequently, the safety latching member 14 is unable to be entirely retracted into the latching member 15. In addition, the boss 14 at one end of the safety latching member 14 is pressed against the tongue-like piece 12c on the passive portion 12b of the actuating piece 12. For this reason, when the actuating piece 12 is forced downwards by the spiral spring 22, the actuating piece 12 fails to reach to the lowest horizontal position, so that the fire-blocking door lock 1 can not be opened as the front of the passive portion 12b of the actuating piece 12 fails to be entirely abutted on the inside of the stop portion 11b of the latch body 11.
Furthermore, when the fire-blocking door 2 is subject to a strike, the latch body 11 will vibrate; so as to make the front end of the passive portion 12b of the actuating piece 12 disengage from the stop portion 11b of the latch body 11. This leads to the problem that both the actuating piece 12 and the latch body 11 fail to press against each other, and consequently the latch body 11 becomes loose and is easily retracted into the latching member 15. Hence, the fire-blocking door lock 1 is unable to maintain the lockup status.
Moreover, if the latch body 11 is intentionally broken, the latch body 11 would then be retracted into the latching member 15 and the fire-blocking door lock 1 would also be unable to maintain the lockup status. In this case, the blocking effect on the fire-blocking door lock could fail.
In addition, a safety release unit 23 is positioned on the fire-blocking door lock 1 adjacent to a side wall of the latching member 15. The safety release unit 23 further includes a retaining ring 26 thereon abutting on a hot-melt tube 24, which is made of a hot-melt material and can be melted away at the temperature of flames. In addition, the safety release unit 23 further includes a spiral spring 25 positioned on the latching member 15. The spiral spring 25 has one end pressed against the side wall of the latching member 15 and has the other end pressed against the protruding inner end 23b of the safety release unit 23. The hot-melt tube 24 is in between the outer end 23a of the safety release unit 23 and the side wall of the latching member 15; the spiral spring 25 is sleeved on the safety release unit 23 in a compressed condition and can generate a backward propulsive force on the inner end 23b of the safety release unit 23. When the fire-blocking door lock 1 is under high heat due to a fire, the hot-melt tube 24 melts away at the temperature of flames, resulting in the blocking effect rendered by the safety release unit 23 without restraint of the hot-melt tube 24. Consequently, the safety release unit 23 is forced to protrude backwards by the elasticity of the compressed spiral spring 25.
In that the inner end 23b of the safety release unit 23 is extended into the latching member 15 and forced against the edge of the recess portion 11a of the latch body, the latch body 11 is not retractable; that is, the latch body 11 can not be withdrawn into the inside of the latching member 15 such that the fire-blocking door lock 1 maintains a secure lockup. This prevents the fire-blocking door 2 from being opened by someone unaware of a fire, thereby preventing burns to people and the spread of flames.
However, when the conventional fire-blocking door lock 1 is under the high temperature of fire, the hot-melt tube 24 positioned on the safety release unit 23 melts away a glutinous liquid; therefore the spiral spring 25 and the safety release unit 23 easily glue together, thus diminishing the backward elasticity of the safety release unit 23. Subsequently, the safety release unit 23 either can not be trusted to enter the recess portion 11a of the latch body 11, or it becomes sluggish, prolonging the reaction time for latching the fire-blocking door 2.
In summary, a variety of drawbacks in a conventional fire-blocking door lock structure cause the problem of failing to surely latch the fire-blocking door lock 1. In addition, the structure is unable to cause the fire-blocking door to be securely closed under the lockup condition, or would lengthen the reaction time for effecting the lockup of the door during-a fire. Moreover, the drawback of failing to maintain the lockup status of the fire-blocking door would seriously affect the fire-blocking effect of the fire-blocking door lock. It is obvious that the drawbacks of a conventional fire-blocking door lock structure with regard to the fire-blocking operation need to be overcome.